1. Technical Field
The present disclosure relates to a system and method for fuel injection in a gasoline direct injection engine during high speed/load operation.
2. Background Art
Direct-injection spark-ignition (DISI) internal combustion engines have been developed to reduce fuel consumption and feedgas emissions of gasoline engines. DISI engines may operate in a stratified charge mode with layers or strata of richer air/fuel ratio near the spark plug and progressively leaner layers below under certain operating conditions, such as low to medium loads and engine speeds and during starting, for example. At higher engine loads and speeds, a stoichiometric or slightly rich homogeneous charge is provided where the air-fuel mixture of the charge is generally well-mixed and homogeneous throughout the combustion chamber.
DISI engines have traditionally used a low-pressure fuel pump in combination with an auxiliary or high-pressure fuel pump to produce injection pressures that provide desired torque while meeting combustion efficiency and emissions targets. More recently, as disclosed in U.S. Pat. No. 6,712,037 for example, gasoline direct injection engines have been developed that rely solely on a low-pressure fuel pump, which provides advantages in terms of lower cost and complexity, but may have reduced cold start performance and reduced maximum torque output at higher engine speeds/loads.
A fuel injection strategy to improve performance during engine startup is disclosed in U.S. Pat. No. 7,234,440, which uses two or more fuel injections for a single combustion event or cycle. During start-up some fuel may be injected during the exhaust stroke with the remaining fuel injected during the intake and/or compression strokes. That strategy includes transitioning to a single injection for normal operation after some number of combustion events have occurred. Similarly, U.S. Pat. No. 7,089,908 discloses modifying valve timing to increase residual exhaust gases and injecting some fuel during the exhaust stroke under partial loading conditions, but transitions to a reference mode with a single injection during the intake stroke at higher speeds/loads.
Under high speed, high load conditions, particularly in applications that rely solely on a low-pressure fuel pump with a side-mounted fuel injector, the injected fuel spray may be deformed by the incoming air stream, which prevents fuel from penetrating across the cylinder and mixing properly to form a homogeneous charge. One method to improve mixture homogeneity, as disclosed in U.S. Pat. No. 6,378,488, uses an intake air deflector in the cylinder head to reduce the influence of the intake air on the injected fuel spray. While this approach may be suitable for many applications, it affects operation across the entire operating range and requires increased complexity in the cylinder head to form the deflectors, which may also impact the cost of the system.